Diffusion pump



Oct. 9, 1945. J. R. o. DOWNING 2,386,299

INVENTOR. JAMES R O- Down 1M6- dew},

AT T ORN'EY Oct. 9, 1945. J. R. o. DOWNING 2,386,299

DIFFUSION PUMP Filed July 3, 1944 2 Sheets-Shoot 2 INVENTOR. O' Dav/mm;

HTTORA/El Patented Oct. 9, 1945 UNITED STATES PATENT OFFICE DIFFUSION PUMP Application July 3, 1944, Serial No. 543,289

7 Claims.

This invention relates to vacuum pumps and particularly to diffusion or condensation pumps useful for increasing the pumping speeds oi mechanical pumps.

An object 01' the invention is to provide such a pump embodying novel principles of construction and operation which provide a more efllcient pumping action than that obtainable with prior pumps. Another object is to provide novel electric governing means for automatically controlling the operation of such pumps.

In the accompanying drawings, which illustrate a preferred form of apparatus according to the invention:

Fig. 1 is a vertical section view 01' the appsratus;

Fig. 2 is a transverse section view on line 2-2 of Fig. 1;

Fig. 3 is an enlarged fragmentary section view of portions of one 01 the vapor chimneys of the apparatus 01' Fig. 1;

Fig. 4 is a side elevation view of one of the baille units 01' the apparatus of P18. 1:

Fig. 5 is a wiring diagram illustrating control circuits.

Referring to Fig. l of the drawings, the apparatus as shown comprises a vertically arranged generally U-shaped duct which forms the pumping passage. As shown this duct is comprised of a pair of conduit sections HI and I! having at their respective opposed ends flanges II and It by which they are bolted together in pressuretight relation. The inlet end of the duct, which is the left-hand end as shown, is provided with a inlet end portion above the throat 22. As shown in Figs. 1 and 3, the upper end of this chimney is fitted with a cup ill having its base web provided with vapor outlet apertures 32 and a central threaded socket for receiving the threaded end oi a pin 34 from which is suspended an inverted conical deflector 38 extending over the top of the chimney. The outer edge of cup is bev eled outwardly and downwardly at 38 and the deflector I6 is spaced slightly above this beveled surface to provide therebetween a restricted channel. Vapors rising through the chimney into cup Ill through apertures 32 escape through this channel into the pumping passage as a continuous jet about the chimney, directed downwardly by the deflector toward throat 22.

The intermediate portion of the chimney 26 which lies within the smaller diameter portion of the duct below threat 2! is provided with a pair of vapor diffusing Jets which, like the preceding jet, are of the so-called umbrella type, each comprising a pair 01' rings oi vapor outlet apertures N in the chimney, a first deflector l2 bolted to the chimney below the apertures 40 and extending upwardly beyond said apertures in spaced relation to the chimney to provide an upwardly directed channel for the vapors, and a second deflector ll, of inverted rustic-conical form, fastened to the chimney above the upper edge oi deflector l2 and extending outwardly and downwardly beyond the upper edge of deflector 42 and in spaced relation thereto. The upper edge of deflector 42 is beveled outwardly and downwardly at It to provide a smooth channel flange II by means of which the duct may be as therebetween and the under surface of deflector fastened into a system to be evacuated. The outlet end bf the duct. which is the right-hand end as shown, is provided with a flange 20 by means oi which it may be connected to the umping port of a suitable backing pump. The inlet end 0 portion of the duct is of enlarged diameter relative to the remainder of the duct and has, at its lower end, a i'rusto-conical throat portion 22 by which it is connected to the remaining portion 01' the duct.

A boiler 24 is provided below the duct from which *a pair 01 chimneys II and II extend upwardly through the adjacent wall of the duct and into the pumping passage. Pumping vapors are conducted by these chimneys from the boiler I into the pumping passage where they are diffused, as will hereinafter be explained.

The chimney It extends upwardly in the inlet branch of the duct, in spaced relation to the ll for the outflow o1 vapors.

The other chimney 28 is provided at its upper end with a nomle ll extending upwardly within the outlet branch of the duct, said nozzle having an internal, upwardly directed vapor outlet passage 5|! which is provided with a'restricted throat 52 between its ends and nearer the inlet end than the outlet end. The upper end of nozzle 48 extends into the mouth of a cooperating tube it fitted into the duct. said tube having an internal passage It directed upwardly and provided between its ends with a restricted throat 58 nearer the outlet end than the inlet end of said passage.

The inlet branch of the duct is encased in a water jacket 80 which extends below the jets oi chimney 28, and the outlet branch of the duct. comprising section i2, is surrounded by a water jacket I2. Cooling water is fed into jacket 60 side walls of the duct, to a point in the enlarged through an inlet pipe 64, from Jacket 60 to Jacket ll through pipe ll, and out through outlet P P I. Pipe I has an enlarged section il in which is contained a thermostatic control switch for a purpose hereinafter described.

The inlet end of the duct is provided with a battle unit comprising a first bame ring ll seated in an internal recess in flange II, succeeding baiile rings 12, ll of successively smaller inner and outer diameter concentrically suspended fromtheprecedingbameringbyrodalfianda baiile plate ll of still smaller diameter suspend edlrombaiilering'ilbyrodsllandimderlyinl the opening in said ring. This arrangement of homes has the desirable eilect ot forcing indrawn gases to spread laterally. between the baiiies. as theyentertheductand itisalsoeilectivetoprevent escape of pumpin vapors rrom the inlet end oi the duct.

The outlet branch or the duct is provided with a bails unit, particularly shown in m. 4. comprisingaseries oi'balieplatesotcircularsegment form mounted in longitudinally spaced relation within cylindrical duct section it above the tube II. The uppermost plate II has its circular edge portion seated in an internal recess in flange 1|, its straight edge being spaced from saidflangetoprovideareduced passageior the flow oi gases out of the duct. From plate 8. is suspended a rod I! upon which are mounted the lower bafle plates It or the unit. Plates ll are otsmallersinethantheplatellandaresc mounted on rod II that their circular edges closely approach the inner periphery of the duct while their straight edge provides a ga between itself and the duct wall for the outward flow of toheatthepumpingliould. redintotheboilertlu'oughaninletpipe I maintainedatalevel slllhtlrabove pumpductandextendingintotheboilerbelow the level or liquid maintained therein.

.&

ed downwardly and outwardlyby deflector It into sage. toward the inwardly slanting throat II o! the duct. Gases from the vacuum system drawn into the inlet 0! the pump are directed outwardly by the inlet baiiles toward the walls or the duct. This has the desirable tendency to concentrate the incoming gases toward the walls at the duct where they are more eflectively entrained, as they flow downwardly, by the vapors from the first let.

The gases entrained'by the vapors diflusing from the first let are thereby compressed into the smaller diameter duct portion below the throat 2! where they are in turn entrained and turther compressed by the higher pressure vapor streams issuing from the two other jets of chimney II. Home of the vapors from each let condense on thecocledwallsci'the passageandthosewhioh donotareentrainedbythe nextsucceedinglet.

The multi-stage vapor diilusion Jets and cool crating pumping passage inlet construction which diminishes in diameter between successive stage lets is highly eii'ective in entraining and initially compressing the gases from the system. It is desirable, as shown. to provide an-inwardiy slanting throat such as throat 22 between the larger and smaller diameter duet portions toward which the vapors from the preceding Jet are discharged.

Vapors from the boiler also rise into chimney I! from which they are directed upwardly by the elector type nozzle II in a first contracting then expanding stream into tube II in which they continue to ilow upwardly toward the i'orepump in a stream which is first contracted then expanded due to the shape oi the tube. The gases and any uncondensed vapors diilused from chimnay flowinto themouthottube lland,intermingled with vapors from ejector nozzle ll. iiow upwardly through the tube being thereby asain heavily. I

The provision oi a last stage let oi the elector type renewing the multi-stage diilusion type Jets at the inlet end is another important feature of the pump, greatly increasing the compression ratie and eilectiveness oi the pump. It is preterahle tosupplyvapors separately tothislaststale .letbyprovidingaseparate chimney torthisiet which may lead from a single boiler feeding all iets.asshown,ornomaseparateboiler.

Vaporsandgasespasnngoutottubellara causedbytheoutletendbailestoiiowangmarly or spirally about the cooled duct wail toward the outlet to the torepump. The vapors condense on tremelylowpressuresathighspeedisrequired.

Pumps that have been made according to the invention, as hereinabove described, when used with a torepump of ordinary pumping capacity theenlargedinletportionotthepmnpingpas- "sucbastwenty-iivecubicteetotairpermlnute,

foreaampleaflOJJLi-otaryoilsefledmechanical pump. readily produce pressures as low as .00001 mm. oi mercury in a properly designed vacuum system free from leaks, vapors and abnormal cutgassins, haves normal pumping speed range. in cubic feet of dry air per minute. from about 25 0. F. M. at 1 mm. pressure to about 20006. 1'. M. at pressures around .0001" mm.- and, at pressures of about .0000! mm., have a normal compression ratio across the pump oi 40.000 to 1. Their performance is considerably superior to that of any other difiusion pump of which I am aware.

For proper operation, I have found it advantageous to maintain the temperature of the pumping vapors flowing from the boiler to the pump substantially constant. To this end, I automatically control the amount or heat supplied to the pumping fiuid in the boiler according to vapor temperature measured by a thermostat in the tube It in the upper part of the boiler. Suitable control circuits for this purpose are diagrammatically shown in F". 6. In this fi re '1 represents a thermostatic switch contained within boiler tube II and set to open and close. at temperatures above and below a predetermined desired vapor temperature, respectively, an electric circuit through wires W and W. I! are cartri ge type electric heaters included in the boiler tubes ll within the pumping fluid, there being eight such heaters, four at each end of the boiler, indicated in the diagram. One terminal of each oitheheatersisconnectedtoawirew. The other terminal of three of the heaters of each bankoffourisconnectedtothewirew'. The other terminal of the fourth or end heater of each bankisconnectedtothe wire W wlresw'and W are respectively connected to the load terniinalsls andlioiamagneticstarterswitchlld whichisconnectedtotheleadsP andPofa single phase power circuit.

when the magnetic switch is closed the three heaters at each end which have their terminals connected to the wires W an W always receive current. However, as the wire W is connected to the circuit, through wire W onl by the thermostatic switch T, the end heaters oi each each set which have their terminals connected across the wires W, W will receive ourrentonlywhiietheswitchlisclosedandare therefore cutin andoutoithecircuitbyopen ingandclosingortheswitch'l'accordinsto variations in vapor temperature.

The particular wstem shown is suitable for operation of 280 volt, 1200 watt cartridge heaters of standard make from a 118 volt, single phase, A. 0. current. Byconneetingonlypartofths heater capacity through the thermostatic switch. extreme fluctuations in vapor temperature are ggs gag 3 2? wheneitheroitheswitches'flor'l'opens. If an automatic shut-oi! control is not desired, the thermostats .l' or 'I may be connected into a circuit with a si nal light or hell.

It will be understood that I have shown and described herein only a preferred embodiment of the invention and that changes may be made in details of the specific construction shown without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a diil'usion pump, the combination of means forming a pumping passage, jet means for diifusing pumping vapor into said passage, a boiler, means for conducting a pumping vapor from said boiler to said let means, means for heating a liquid in said boiler to supply pumping vapor to said conducting means. and thermostatic control means interposed in the path of flow of said pumping vapors to said jet and connected to said heating means to regulate the heating of said liquid by said heating means in response to changing temperatures oi said vapor.

2. In a dlflusion pump. the combination of means forming a pumping passage, let means ior diffusing pumping vapor into said passage, a boiler, means for conducting a pumping vapor from said boiler to said let means, means for heating a liquid in said boiler to supply pumping vapor to said conducting means, and thermostatic control means responsive to temperature change changes within said boiler and connected to said heating means for regulating the operation thereof to maintain the temperature of the pumping vapors leaving the boiler substantially constant.

8. In a diflusion pump. the combination of means forming a pumping passage, let means for diliusing pumping vapor into said passm. boiler means, means for conducting a pumping vapor from said boiler means to said let means. means for heating a liquid in said boiler means tosupply said pumping vapor to said conducting means. and means for automatically regulating the operation ofgaid heating means according to the temperature of said vapor flowing to said jet means :to niaintain said temperature substantially con- 4. In a diilusion pump, the combination claimed in laim 3, wherein said heating means includes anelectrically operated heater and said regulating means includes a thermostatic switch connected in the electric} power circuit to said heater and interposed in the path of flow of vapor from said liquid to said let means to open and close said circuit at predetermined temperatures oi said vapor.

5. A diiiusion pump having, in combination, a vertically dispoud duct forming a pumping passage having an inlet at the upper end. a pumping fluid boiler below said duct, a tubular vapor chimneyrising i'romsa'idboilerintosaidpassage, and let means for discharging pumping vapors'irom said chimney into said passage comprising a horizontal row 01 apertures through said chimney wall, a first deflector extending outwardly from said chimney below said aperwardly from the chimney above said first defiector in spaced relation to the upper edge of said ilrst deflector and providing between itself and said first deflector a downwardly directed channel for the escape of vapors irom between said first deflector and the chimney into said pumplng m- 6. A vapor pump as claimed in claim 5 wherecent the outlet end thereo! and balls means in said passage adjacent the outlet end thereof, said bame means comprising a series of plates within said passage extending transversely and spaced longitudinally thereof, said plates each providing a reduced opening between the center and a side wall oi said passage for the ilow of a stream of vapors and gases toward said outlet end. and said plates arranged with said openings provided by successive plates staggered less than 180' about the axis of said passage to produce an angular flow of said stream along said passage wail.

J. R. 0. W6.

CERTIFICATE OF CORRECTION Patent No. 2,586,299-

October 9, 1914.5.

JAMES R. O. DWNINGF It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page5, first column, line he, strike out the word "eacli' first occurrence; and second column, line 52, before "changes" strike outlchange"; and" that the said Letters Patent should he read with this correction therein that the same may conform to the record at the case in the Patent Office. Signed and sealed this 18th day of December, A. D. 1915.

(Seal) Leslie Frazer First Assistant Cumiesioner oi Patents.

ilrst deflector and providing between itself and said first deflector a downwardly directed channel for the escape of vapors irom between said first deflector and the chimney into said pumplng m- 6. A vapor pump as claimed in claim 5 wherecent the outlet end thereo! and balls means in said passage adjacent the outlet end thereof, said bame means comprising a series of plates within said passage extending transversely and spaced longitudinally thereof, said plates each providing a reduced opening between the center and a side wall oi said passage for the ilow of a stream of vapors and gases toward said outlet end. and said plates arranged with said openings provided by successive plates staggered less than 180' about the axis of said passage to produce an angular flow of said stream along said passage wail.

J. R. 0. W6.

CERTIFICATE OF CORRECTION Patent No. 2,586,299-

October 9, 1914.5.

JAMES R. O. DWNINGF It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page5, first column, line he, strike out the word "eacli' first occurrence; and second column, line 52, before "changes" strike outlchange"; and" that the said Letters Patent should he read with this correction therein that the same may conform to the record at the case in the Patent Office. Signed and sealed this 18th day of December, A. D. 1915.

(Seal) Leslie Frazer First Assistant Cumiesioner oi Patents. 

